Steps to Reproduce
Place a hopper or other container and put a renamed item in it. In my case I used a hopper and a piece of paper renamed "12345"
I ran the following command:
/execute if block 0 103 -29 minecraft:hopper{Items:[{id:"minecraft:paper",tag:{display:{Name:"53623"}}}]} run say hi
And since the command failed, it did not say hi.
This syntax worked in 17w50a, but now no longer works. Removing the display name argument allows the command to run successfully once again.
Item display names were upgraded to text components now, so you might have to try
or something similar